MicroRNAs (miRNAs) are a group of endogenous ˜21-23 nt noncoding RNAs. They regulate expression of genes at the posttranscriptional level (Bartel, 2004 Cell, 116(2):281-97). Although only recently discovered, they have been found to play key roles in a wide variety of biological processes, including cell fate specification, cell death, cell proliferation, and fat storage. So far, more than 300 different human miRNAs have been identified (Griffiths-Jones, 2004, Nucleic Acids Res. 32 D109-111). Most of them are thought to recognize their mRNA targets via partial antisense complementarity. This partial complementarity, as well as the short lengths of miRNAs and their targets, makes identification of novel miRNAs difficult by conventional sequence comparison methods. Thus, there is a need for a novel approach for identifying miRNAs and their targets.